In many situations where trusses, girders, or beams are needed a conventional solid beam is unsuitable. It is essential that the structural member used be more lightweight, especially in those cases where transportation presents difficulties. It may be further desired that the element be collapsible to a compact size, and, finally, readily erectable upon arrival. These considerations are particularly crucial for operations in outer space, such as construction of antennae or space platforms. Transportation is feasible only for those materials which are lightweight and compact. The addition of each unit of mass or volume is extremely expensive. Whiles such a strong and rigid structure might be provided by a combination of rods and cables, the assembly of a structure in outer space poses such acute problems that preassembly is also necessary.
A prior art approach to this problem has been the use of semiflexible curved metal sections which can be flattened and rolled up without strain by a special reel, and which snap into a self-supporting configuration when let out. One such example is U.S. Pat. No. 3,503,164 which teaches a pair of semi-circularly curved sections joined by hinges along their lengths. Such an arrangement has the drawback of being heated on one side by the sun's rays and not on the other, causing it to bend. This problem can be avoided if the beam includes open spaces as in U.S. Pat. No. 3,564,789. Another problem remains; although strategic design of cross-braces and curved longerons yields a fairly high moment of inertia, the overall rigidity of the beam must be compromised by the requirement that the beam be pressed flat by the reeling mechanism.
Another attempt to provide a solution has been in the use of a set of semirigid rods, any one of which could be rolled up with the application of moderate force, as in U.S. Pat. No. 3,474,579. The set of rods, when disposed parallel to each other and in a common plane, can be rolled up by a force which is simply the force needed for one multiplied by the number of rods. When the plane of the rods is curved into a cylinder, the resulting moment of inertia is much greater. Nonetheless, considerable force is required to roll up such a structure.
It is thus seen that there remains a need for a structure featuring the required qualities of strength, light weight, and compactness as explained above, yet which can be deployed quickly and without the use of substantial force.
It is an object of the present invention to provide a more conveniently usable structural member.
It is a further object of the invention to provide a structural member which is strong, lightweight, and compact.
It is a further object of the invention to provide a structural member which can be reduced in one or more dimensions for transportation.
It is a further object of the invention to provide a structural member consisting of a series of longitudinally rigid segments which may be rotated or held fixed in relation to each other.
It is a further object of the invention to provide a structural member comprised of a series of segments wherein the segments are able to rotate relative to each other through the use of pivotal connections between the segments.
It is a further object of the invention to provide a structural member wherein the segments of the member may be held in fixed relation to each other by the use of a tensioning means.
It is a further object of the invention to provide a structural member which may be stowed for transportation by folding it around a cylinder.
It is a further object of the invention to provide a structural member which may be folded a multiplicity of times around a cylinder.
It is a further object of the invention to provide a structural member which may be stowed and deployed with a minimum use of force.